Computer simulation of Pb and Sr isotope evolution of the Earth's crust and upper mantle

摘要: Abstract Isotope evolution in a differentiated (crust and upper mantle) chemically heterogeneous Earth has been computed for model with isotopic exchange between crust mantle at an exponentially decreasing rate. To simulate the effects of subduction, cells are selected random, their contents mixed then redistributed into from which they came—to give new but momentarily isotopically homogeneous systems. Daughter isotopes each cell grow according to equations appropriate closed chemical Rock age distributions data created by computer calculation mimic nature. Pb isotope changes through geologic time illustrated demonstrate that two-stage interpretations applied rocks complex histories may be misleading. The intercept ore growth curve regressions fit gives minimum values only duration U systems, not when distribution first occurred. An derived about 3 b.y., system is shown quantitatively compatible average Rb Sr crustal 1.5 b.y. constant degree heterogeneity all history.